ENCRINAL LIMESTONE. 
145 
pi. 13 of the Silurean Researches. Ortlris liyhrida, O. canalis, Atrypa rotunda, A. linguifera 
and several others. Spirifer? pisum (Silurean Researches , pi. 13, f. 9) is identical with a 
fossil found in this rock. 
This rock is the lowest position yet known where the remains of fishes have been found. 
A specimen of the defensive fin bone (Ichthyodorulite) of some unknown species, more than 
eight inches long and imperfect at both ends, has been found in this rock. Its greatest 
breadth is about one inch, and a transverse section presents the form of two very acute tri¬ 
angles with their bases in contact, forming the centre of the bone. 
I have lately seen some fossils from near Point Abino in Canada, which appear referable to 
forms found in this rock in the Third District, particularly the Atrypa Icevis of Mr. Vanuxem. 
Since this rock is not known to extend within the Fourth District, no illustration of its 
numerous and beautiful fossils are given. 
16. ENCRINAL LIMESTONE. 
Scutella Limestone of the Annual Reports . 
(Part of No. 6, Pennsylvania Survey.) 
This mass has no existence in the Fourth District, thinning out east of the central part of 
the State, and appearing in force only in the region of Schoharie and the Helderberg. 
It contains a great abundance of a flat or saucer-shaped pelvis of a crinoid, from the re¬ 
semblance of which to the Scutella it received the name, Scutella limestone. Broken co¬ 
lumns and other remains of Crinoidea, in a perfectly crystalline condition, are very abundant 
in this rock. 
17. UPPER PENTAMERUS LIMESTONE. 
(Part of No. 6, Pennsylvania Survey.) 
This mass succeeds the last, resting directly upon it. Mr. Gebhard junior, of Schoharie, 
has clearly demonstrated that by its peculiar assemblage cf fossils it is distinguished from any 
other rock. Among these, is a species of Pentamerus, in shape like P. Galeatus, but quite 
smooth, and evidently a distinct species. Several forms of Atrypa also occur in this rock, 
very similar to those below. 
The thorough practical acquaintance of Mr. Gebhard with all the rocks of this part of the 
system, and his nice discrimination of their fossil contents, renders his opinion decisive in 
such distinctions. 
Geol. 4th Dist. 
19 
